This invention relates to a protective coating for a color filter used in a full color liquid crystal display device or the like and the method of manufacturing such protective coating.
Full color liquid-crystal displays have become very common, in recent years, as flat panel displays. They generally have a structure comprising: a color filter, a counter electrode substrate facing the color filter, and a liquid-crystal layer provided in a gap between the color filter and the counter electrode substrate. The structure of the color filter is arranged so that a colored layer of a black matrix and a plurality of colors (generally three primary colors, red (R), green (G) and blue (B)) is provided on a transparent substrate and a protective layer and a transparent electrode are stacked thereon in that order. These color liquid-crystal displays are constructed so that a color image is obtained by controlling the light transmission of the liquid-crystal layer in its portions corresponding to pixels of respective colored layers R, G and B.
In the color filter, the protective layer functions to protect and flatten the colored layer. In general, color liquid-crystal displays have a problem that the presence of an uneven gap attributable to the waviness of the surface of the transparent substrate in the color filter, an uneven gap among R, G and B pixels, or an uneven gap within pixels of R, G and B lowers the flatness of the transparent electrode. This causes uneven colors and uneven contrast, leading to lowered image quality. In particular, in color liquid crystal displays of super-twisted nematic (STN) system, the flatness greatly affects the image quality. This renders flattening by the protective layer very important.
In use, the color filter is adhered to the counter electrode. The assembly is then tested for display quality. In consideration of the reusability of the color filter when the assembly is judged to be unacceptable in the display quality test, the protective layer is preferably provided only in specific regions so as to cover the colored layers on the transparent substrate. To this end, the protective layer has been formed using a photocurable resin that permits portions to be cured to be easily limited through a mask.
In the formation of the protective layer using the conventional resin, an organic solvent has been used in the development after exposure of the radiation curable protective coating material to UV radiation. This is troublesome in handleability and wastewater treatment and further lacks in profitability and stability. European Patent Application Publication No. 977,085 describes a photocurable resin designed to solve this problem. A photocurable resin is described which, by virtue of the introduction of an acidic group into the photocurable resin, permits alkali development after exposure. The photocurable resin composition comprises: a copolymer resin; a bifunctional or higher polyfunctional photopolymerizable acrylate monomer; an epoxy resin and an initiator.
This invention relates to a curable adhesive article comprising a curable pressure sensitive adhesive layer coated on a transparent carrier film. The adhesive article is useful in forming a protective coating on a color filter. The adhesive article may be a tape or a label and may also include a curable epoxy layer between the curable pressure sensitive adhesive layer and the transparent carrier film. In another embodiment, a radiation curable pressure sensitive adhesive layer is a removable adhesive that may be used to position a radiation curable epoxy layer on a color filter. The radiation curable epoxy layer and radiation curable pressure sensitive adhesive are exposed to radiation through a mask positioned over the colored layers of the color filter. The radiation exposure transforms the pressure sensitive adhesive from a removable adhesive to a permanent adhesive. The uncured epoxy layer portions and the uncured adhesive portions are removed with the removal of the carrier film. The remaining multilayer structure is then baked to fully cure the epoxy layer and to transform the adhesive further into a near structural adhesive. In one embodiment, the fully cured epoxy and adhesive layers together make up the protective coating for the color filter. In another embodiment, the fully cured adhesive layer itself makes up the protective coating for the color filter.
The adhesive article of the present invention comprises: (a) a radiation curable adhesive layer having an upper surface and a lower surface, the adhesive layer comprising an acrylic pressure sensitive adhesive and optionally, an acrylated urethane oligomer; and (b) a transparent carrier layer, having an upper surface and a lower surface, wherein the lower surface of the transparent carrier layer overlies the upper surface of the adhesive.
The adhesive article of the present invention may also comprise: (a) a radiation curable adhesive layer having an upper surface and a lower surface, the adhesive layer comprising an acrylic pressure sensitive adhesive and an acrylated urethane oligomer; (b) a radiation curable epoxy layer having an upper surface and a lower surface; and (c) a transparent carrier layer, having an upper surface and a lower surface, wherein the lower surface of the transparent carrier layer overlies the upper surface of the epoxy layer and wherein the lower surface of the epoxy layer overlies the upper surface of the adhesive layer.
The method of manufacturing the protective coating on a color film of the present invention comprises the steps of: (1) adhering an adhesive article to the color layer of a color filter, wherein the adhesive article comprises (a) a curable adhesive layer having an upper surface and a lower surface, the adhesive layer comprising a crosslinkable acrylic pressure sensitive adhesive; and (b) a transparent carrier layer, having an upper surface and a lower surface, wherein the lower surface of the transparent carrier layer overlies the upper surface of the adhesive; so that the lower surface of the adhesive layer is adhered to the upper surface of the colored layer; (2) curing the adhesive layer of the adhesive article; (3) removing the carrier layer to form a multilayer structure comprising a transparent substrate, a colored layer and a protective coating overlying the colored layer, wherein the protective coating comprises the cured adhesive layer.
The method of manufacturing the protective coating of the present invention may also comprise the steps of: (1) adhering an adhesive article to the color layer of a color filter, wherein the adhesive article comprises (a) a radiation curable adhesive layer having an upper surface and a lower surface, the adhesive layer comprising an acrylic pressure sensitive adhesive and an acrylated urethane oligomer, (b) a radiation curable epoxy layer having an upper surface and a lower surface; and (c) a transparent carrier layer, having an upper surface and a lower surface, wherein the lower surface of the transparent carrier layer overlies the upper surface of the epoxy layer and wherein the lower surface of the epoxy layer overlies the upper surface of the adhesive layer; so that the lower surface of the adhesive layer is adhered to the upper surface of the colored layer; (2) positioning a photomask over the adhesive article; (3) exposing the adhesive article to radiation through the photomask to cure portions of the adhesive layer and the epoxy layer of said multilayer tape and leaving portions of the adhesive layer and epoxy layer uncured; (4) removing the carrier layer and the uncured portions of the adhesive layer and epoxy layer to form a multilayer structure comprising a transparent substrate, a colored layer and a protective coating overlying the colored layer, wherein the protective coating comprises the radiation cured portions of the adhesive layer and the epoxy layer; and (5) baking the multilayer structure to fully cure the protective coating.